GMM with missing data

Hi all,

I have been working on applying growth mixture model to psychology data with missing data. I know I can use existing software to deal with the missing data. But I want to understand the math behind of it. There is one paper for the Growth mixture model detailing the math titled "Finite Mixture Modeling with Mixture Outcomes Using the EM Algorithm". I want to know the methodology of the growth mixture model with missing data. Can anyone show me the math or which paper should I refer to?
Thanks a lot.